My car occasionally idles very rough (usually after getting off the freeway), enough that the engine slams side to side hard enough to shake the whole car and the a/c lines would hammer against the frame rail before I replaced the motor mounts. I think I finally figured out what is causing it, but I don't know where the problem is.

When the throttle linkage is in the idle position, there is some play in the stop lever if you move it back and forth, and if you move the stop lever toward the valve cover enough to take up the slack in the linkage the car idles smooth, but if you move it the other way the engine starts shaking violently. I am not sure if that makes sense, but the problem is excess play in the linkage rather than something sticking so it doesn't always return quite all the way to idle. I have only ever seen one properly running om617 and that was a couple years ago, so I am not exactly sure where something might be wrong with mine.

Video?

Do you have issues only when at operating temps?

Moving the lever toward the valve cover should, eventually, shut off the engine, does this occur?

Mercedes-Benz 126 Service Manual Library

The link is for your car, should have the linkage lengths in there.

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83 SD

84 CD

Hard to say exactly what is really going on here. If moving the shut off a little towards the shut off position vastly improves the idle.

The shutoff is linked to the rack in the pump. Rack damper bolt adjustment perhaps when the engine is hot? On inspection it may even need a new one.

Can you post photos of your linkage? So we can see if anything is worn out?

What brand motor mounts did you use? Did you replace the transmission mount?

Last valve adjustment? Fuel filter change? Injectors changed?

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Idle problems that show up when the car is hot can have a number of causes. However, what you described is a loping, rhythmic shake at idle (as opposed to more of a harsh, 'miss' vibration), which is a typical indicator of a rack damper bolt issue.

The rack damper bolt must be adjusted when the engine is hot, preferably after at least 15 minutes of highway speeds. (I have done it in gas station parking lots, mall parkades, etc.)

Also the idle setup on these cars, as they age, is a balance of idle speed adjustment and rack damper bolt adjustment. Some are harder than others to find the 'sweet spot' on. In some instances you have to play with the idle speed in order to get a nice smooth rack damper adjustment. I had one SD where it took five runs at it (you only have so much time, after the highway run, to work with the motor nice and hot).

If your rack damper bolt is silver it is the original and you may need to install the later, gold model which was an upgrade. The original silver ones were found to be a bit too short to function properly as the cars got older. Shop around as others have found that prices vary hugely from various sources.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

My lever is tight.

Inspect the pictured areas.

Haven't worked it back and forth tho.

Attached Thumbnails

   

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The shutoff lever does operate correctly, when I was talking about moving it back and forth I meant just the slack in the linkage. My odometer doesn't work and I don't know how to fix it, so I don't know the exact mileage, but the valves were last adjusted within the last 2 months, and the fuel filters within the last year. Im not sure on the injectors, probably once in the last 400k miles at some point. The motor mounts were the OE supplier brand pelican sells (phoenix i think? They have a mark where the mercedes start was removed), I didn't change the transmission mount though.

The idle problems are not only when hot, and very intermittent, although it very often is the worst after getting off the freeway. It both has the loping idle where the engine slams back and forth enough that the engine probably moves side to side more than 3/4 inch if you measured at the valve cover, and also vibrates enough that it has broken the air cleaner mounts off, then snapped the bracket after I replaced them, then vibrated the top nut off the air cleaner within a couple days after I put a new bracket on.

I will try to take pics and a video of it this weekend. I don't know anything about the rack damper bolt other than its a part of the injection pump adjustments, so I will have to research that more to figure out what it looks like and how the adjustments are supposed to work.

The rack damper bolt/pin (previous long discussion) will show itself only when the engine is hot, so put that on the back burner.

The violent shaking, this is an indication of the RD bolt/pin tho, so that may be a contributing factor. Does that violent shake happen anytime also?

Some of these engines shake more than others.

I'll try and replicate the part about pulling the stop lever. I would think, however, it won't pull back without a bunch of force.

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Engine has the Jerry E Lewis disease.? Whole lot of shaking going on? A telling symptom is your bones rattle apparently.

The few occasions that I have no ideal of what is going on. Doing a check of everything or general tune up has saved my posterior. During the process something abnormal has surfaced. Not on mercedes diesels but there is no reason they should not respond.

We do not have a compiled list of what is a general tuneup to my knowledge. Too many people believe a diesel never needs one. Still many of these cars have remained running with almost nothing done for a very long period of time.

A new owner may not even realize the valves are adjustable since hydraulic lifters have been around seemingly forever now. You have checked your valve adjustments? Many of these cars went an unknown distance since the last time they were done.

It can ultimately present problems even of your nature. These engines ask little and even that is not done from my experience on the ones I have purchased usually for a very long time if ever.

Made this video this morning:
https://www.youtube.com/user/Cane1994M

Not supposed to be able to pull back on the stop lever.

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Now that I posted about this, the car has been idling perfectly so I haven't been able to make avideo showing the problem. Whatever it is it is very intermittent, so determing if it goes away for good will be hard. I think for now I am going to replace the large white bushing in the above picture because it is noticeably worn, and recheck the valve clearances and adjust if needed.

Sounds like a plan - when you have it in bits make sure the return spring at the IP is doing its job properly.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

When owning diesels I find it is advisable to keep an open mind. For example a load of marginal fuel is not all that unusual. I find it especially disturbing if I have a potential problem and it self clears.

Once for example my powertrain in the 77 300d developed a clanging towards the rear lower portion of the engine. I thought this is just great as the flexplate was my first suspicion. Then it stopped and has never come back. There is not a lot of logic in these things sometimes.